The invention relates to an apparatus for coating workpiece surfaces, for example condenser films, with a coating material that is to be evaporated, especially pure aluminum, the coating material being fusible in an evaporator cell disposed in a vacuum chamber and being fed in the form of a piece of wire from a supply spool of wire to the evaporator cell in accordance with the depth of the molten bath, and being delivered between a motor-driven shaft and a roller providing counter-pressure, in the manner of a capstan drive.
It is common in film vapor depositing apparatus to combine a plurality of evaporator cells to form a so-called evaporator bank and to dispose this evaporator bank in the vacuum chamber in the direct vicinity of the film that is to be coated, and to draw the material that is to be evaporated in the form of wires from supply spools and transport them and feed them to the evaporator cells with the aid of friction wheeldrives. (U.S. Pat. No. 3,488,214, German Patent Disclosure Document 34 28 651, U.S. Pat. No. 2,664,853, U.S. Pat. No. 3,970,820).
Experience shows that a particular difficulty consists in making sure that the wire feeding devices of all of the evaporator cells arranged side by side and forming the evaporator bank are controlled according to the depth of the molten metal in each evaporator cell. The mechanical and electrical devices necessary for this purpose are generally of very complex design (see the apparatus according to U.S. Pat. No. 3,970,820), especially because the individual feeding devices have to be electrically insulated from one another.
If the wire evaporator consists of a band coating apparatus consisting of a plurality of individual evaporators driven by a common shaft (see EP 0,084,126) the common drive shift feeding the wire must be insulated electrically between each pair of feeding devices; this is because of the different electrical voltages that are applied to the individual evaporator cells. The drive shaft is therefore generally divided into a plurality of sections (according to the number of evaporator cells provided on the evaporator bank) and these shaft sections are joined by couplings of an insulating material.
An apparatus for the continuous coating of substrates in band form is known (DE 40 27 034), which is equipped with a plurality of evaporator boats of about the same size and configuration, forming an evaporator bank and arranged lengthwise of the direction of band movement and parallel to one another at approximately equal distances apart. The evaporator boats are all made from an electrically conductive ceramic and can be heated by the direct passage of current through them, and a device is provided for the continuous feeding of the wire to be evaporated to the evaporator boats. See also U.S. Pat. No. 5,242,500, incorporated herein by reference.
These individual evaporator boats of the evaporator bank are each arranged offset from one another, while all evaporator boats together cover a narrow coating zone running transversely of the direction of band movement.